Spark plug



Dec. 2, 1930. P. o. STEWART SPARK PLUG Filed Jan. 18, 1930 INVENTOR Pazierdon afitewarl QM MNWH ATTORNEY Patented Dec. 2, 1930 UNITED sTArs arser orricr:

PATTERSON o. s'rnwnnnfor NEW YORK, 1v. Y.

SPARK rLue Application filed January 18,1930/Seria1 No. 421,745.

The present application is inpart a di vision of the application for anti-fouling spark plugs, filed Dec. 6, 1926, Serial No. .14

152,925, and the present invention relates to spark plugs for internal combustion engines, especially for those having relatively low initial compression, and more particularly to the structure and insulation of spark plug electrodes, whereby fouling of the spark 1o plug by carbon is minimized.

An important feature of the invention 'is the provision of an annular insulating surface of relatively narrow width, separating a grounded and an ungrounded electrode,

which has a beveled edge that approaches the coacting electrodes as it recedes from the face of the insulator.

A further feature of the preferred form of the invention is themountingof the grounded electrode on a disk or 'flange-like'section at the bottom of the insulator.

Other and further features will be apparent to one skilled in the art after a study of this specification taken in connection witl the attached drawings, wherein Fig. 1 is a longitudinal central part sectional view of the device, shown partly in elevation, with the cap removed;

Fig. 2 is a bottom plan view of the device, shown in Fig. 1;

Fig. 3 is a sectional central view of a modified form of the device.

Referring to Fig. 1, the body or core of r the spark plug, which is of suitable insulating material, is provided at its upper portion with a central chamber 11,having at its bottom the bore 12, extending through the lower portion of the body and terminating at the tapered end 13 of the body.

The body or core 10 is received in the shell 14 of the spark plug, being held therein by the threaded metal gland 15, the body 10, having the enlarged portion 16, a packing ring 17 being disposed between the upper side of the portion 16 and the lower end of the gland and a packing ring 18 being disposed between the lower end of the portion 16 and the ledge 19 of the shell 14, for preventing loss of compression. The tapered end both appurtenant to the insulator, one of 13 of the body 10 is located in the chamber 20, formed by the lower portion of the shell The chamber 11 may contain a frequency change as shown in Fig. 1 of nyabove application,.on the usual enlarged portion of the electrode stem. V i

The usual metal electrode stem 29 is received in the bore'12, and has at itslower end the sparkii'ig member or head 30 spaced away somewhat from the tapered end 13 of the body 10, the stem 29 and head 30 constituting the ungrounded electrodeof the spark plug. Rings 31 of pliable insulating material, such as mica, are arranged in overlying and underlying relation around the stem 29 in the above mentioned space, the outerimarginal portions of theserings being located in the flanged recess-forming portion 32 of the metal ferrule 33, which is connected to the shell 14. by the metal strip 34, this ferrule constituting the grounded electrode of the spark plug.

By referring to Fig. 1, it will be noted that the circular head 30 of the stem29 is bevelled outwardly and downwardly from its top edge at its bottom edge and that its bot tom edge is'in substantially the same horizontal plane as the lower end of the annular end portion 35 of the ferrule 33, a gap being formed between the head 30 and the annular end 35 of the ferrule 33 and of least width between the bottom edge of the head 30 and the bottom edge of the annular end portion 35, the intention being that sparks passing across said gap from the head 30 to the ferrule 33 shall pass from various parts of the circumferential edge of the head 30 and not be confined to any particular part of the head 30.

It will be noted that Fig. 1 shows the rings 31 as separate pieces from the main insulating body 10, rather than integral with the tapered end 13 of said body 10, but the invention is not thus limited; and as shown in the modified form of the device of Fig. 3 the flange like portion 31 is integral with the lower part 13 of the insulating body 16a, and the parts 10 and31 of Fig. lmay be consid ered as constituting one insulator. The up per part of the body is tapering'upwardly as at and the bore therethrough 12 extends from end to end thereof.

A rod 29 extends through the entire length of said body 10a and terminates at the upper end thereof in a threaded portion 26, for connecting said rod 29 to suitable electric terminals.

The tapered part 13 at the lower end of the insulating body terminates at the lower end thereof in a flange like portion or head 31, encompassed by a metal shell 36, which terminates at the lower end thereof in a ring shaped member 35, encompassing the head of said rod 29; a bridging strip 3%" conneets said ring to the lower edge of said shell 14.

The operation of this invention in use in a motor properly adjusted and not pumping oil is practically the same any spark plug of conventional design, but for illustration, say, the motor starts to pump oil and the carburetor supplies a mixture slightly overrich in fuel content, then at once the walls of the combustion chamber, including the pertions of the spark plug exposed to the explosion flame, are subjected to carbonizing, the partially burnt excess lubricating oil acting as a binder and forming with the uneonsumed portion of hydrocarbon in the mixture an amorphous carbon; this carbon'in forming on the insulator of a spark plug of conventional design, acts as a high resistance leak between the electrodes and, as the carbon coating gets thicker from continued operation, the resistance is lowered until the plug ceases to lire, whereas with a spark plug designed as herein described the action is entirely different, as will be described.

Referring to Fig. 1 of the annexed drawings it will be observed that the insulating space 31a between the grounded electrode 33 and the head 30 ot the ungrounded electrode is very narrow, being in fact only a few thousandths of an inch wider than the spark gap; as the carbon forms on this narrow insulating space suliieiently to lower its resistance to or below that of the spark gap the current will flow across at that point; but this high resistance short being so narrow the current will heat the carbon to ineandescence and it will therefore be dissipated or consumed,

As can be seen, this structure allows the insulating space 31a to be kept at a comparatively hi h temperature by the explosion flame tending to vaporize or dry any oil that might be deposited thereon.

The invention is presented as including also such modifications and changes as may properly come within the following claims.

I claim: I

1. In combination, an insulator, an electrode stem in said insulator, provided at its outer end with a circular electrode head, having thereon an outer circular sparking edge, spaced from said insulator and of greater diameter than the inner edge of the head, and an annular metal ferrule at the lower end of said insulator and spaced from the periphery of said head, said ferrule having thereon an annular electrode portion, having its outer edge in the plane of said sparking edge to form therewith an annular sparking gap the distance between said electrode portion and head being minutely greater at the edge of said head, adjacent to the insulator,

than at said sparking edge; whereby said electrodes when in use are separated by a very narrow annular space, which is at all parts only minutely wider than the sparking width at the lower end thereof.

2. In a spark plug an insulating body, a downwardly tapering portion at the lower end, thereof, a metal shell, enclosing said body, the lower end of said shell forming a chamber therebetween and said tapering portion, an electrode stem in said body, having at the outer end thereof a disk shaped electrode head, having thereon a circular sparking edge, and an annular metal ferrule, at the lower end of said body and spaced from the periphery of said head, said ferrule having thereon an annular electrode portion, having its outer edge in the plane of said sparking edge, to form therewith an annular sparking gap, whereby said electrodes when in use are separated by a very narroi i annular space, and said exposed tapering portion serving to be highly heated in low pressure eugines, thereby eliminating deposits of oil.

Signed at New York in the county oi New York and State of New York, this 16th day of January, A. D. 1930.

PATTERSON O. STElVART.

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